During the global clade II mpox outbreak, cases have disproportionately affected gay, bisexual, and other men who have sex with men (MSM). Cruise ship travel-associated mpox infections have not been previously described. During January 25-April 18, 2024, CDC was notified of eight mpox cases among cruise travelers on four ships: four among crew members and four among passengers. Seven cases were laboratory-confirmed as clade II Monkeypox virus. All exposure histories indicated male-to-male sexual contact. No patients were hospitalized, and none died. Crew members with mpox received their diagnoses on board and were isolated while infectious. Contacts were identified, monitored, and assessed for mpox postexposure prophylaxis (mpox vaccination). No crew members with mpox had been vaccinated against mpox. Passengers with mpox received their diagnoses after cruising on voyages marketed to gay and bisexual men, with symptom onset dates suggesting voyage exposures. For one cruise ship, two of the three reports of mpox among passengers were received after health departments were notified of potential cruise-associated exposures, and letters were sent to other passengers. Three of the four passengers with mpox had received 2 doses of JYNNEOS vaccine in 2022. Cruise lines should consider educating crew members on symptoms, risks, and preventive measures related to mpox and working with medical personnel to facilitate mpox vaccination as preexposure prophylaxis for eligible crew members. Cruise passengers who are eligible, predominantly MSM, should receive mpox vaccine before cruise travel. For cruise voyages marketed to gay and bisexual men, having mpox vaccine available on board would facilitate timely postexposure prophylaxis, if indicated; mpox prevention messaging and education before and during a voyage are also recommended.